THAW DEPTH CHARACTERISTICS OVER 5 THAW SEASONS FOLLOWING INSTALLATIONOF A SIMULATED TRANSPORT CORRIDOR, TULITA, NWT, CANADA

A simulated transport corridor or right-of-way (ROW) and pipeline tren ch were constructed in a decadent Picea mariana stand underlain by per mafrost 10 km north of Tulita, NWT. Between 1986 and 1990 thaw depth w as monitored. Initially, the mean thaw depth in the undisturbed contro l forest was 35.0 cm (19 August 1986). By 1990, thaw depth had increas ed by 75% (26.4 cm) in the control forest, by 212% (74.3 cm) on the RO W and by 320% (111.9 cm) in the trench. The rate of increase slowed in 1990 with the result that the trench had its greatest mean thaw depth in 1989 (162.7 cm). The 1990 reduction in the increase of thaw depth was attributed to a relatively cold year (mean daily air temperature: -6.4 degrees C). Mean daily ground surface temperatures during the 199 0 observation period (February to August) ranged from -4.0 to +19.9 de grees C in the control forest and from -3.3 to 26.0 degrees C in the t rench. Thaw depth increased mainly due to the combined efforts of an i ncrease in ground temperatures associated with surface alterations on the ROW and trench and an overall regional warming trend that affected the disturbances as well as the control area. (C) 1998 John Wiley & S ons, Ltd.